Acetabularia ryukyuensis

Thallus in clusters, umbrella-shaped, moderately calcified, to 7 cm high. Discs bright green to dark green, to 1.5 cm diam., cap coneshaped when young and cap-shaped when older, of 62-72 rays. Outer margins of rays rounded or truncated. Corona superior (on dorsal side of the disc, at the base of rays) consist of oblong projections, 37 mm diam., 175 mm long, with 5-7 hair scars, 12-20×20-25 mm. Corona inferior (underside base of rays) consist of palisade-like projections, 180-200 mm long, 180-200 mm wide at base and 50-60 mm wide near round apices. Stalk grayish-white, to 7 cm high, 300 mm diam. at base and 500 mm above, heavily calcified. Rhizoids to 1 mm long, branched irregularly dichotomously. Immature thallus consists of long stalk with series (5-6 levels) of hair scars below and whorls of branching filaments above. Growing on stones, mostly on coral fragments and blocks, on dead shells in shallow sheltered pools and in the upper subtidal.

Japan (Ryukyu Archipelago), Philippines.